Hepatocellular carcinoma (HCC) is one of the most common causes of cancer-related deaths world-wide. In spite of its relatively low occurrence in the U.S., its incidence is predicted to accelerate during the next decades. Research is proposed to evaluate in vivo a newly designed, targeted, prodrug therapy for cancers that overexpress the carboxylesterase, CES2, with focus on HCC. The therapy is based upon doxazolidine, a formaldehyde conjugate of doxorubicin that is more than an order of magnitude more active against a variety of both sensitive and resistant (MDR phenotype) cancer cells than doxorubicin. Doxazolidine induces cancer cell death by a different mechanism and is less toxic to cardiomyocytes than doxorubicin. The prodrug of doxazolidine, N-(pentyloxycarbonyl-p-aminobenzyloxycarbonyl)doxazolidine (pentyl PABC- Doxaz, PPD), is activated by CES2 present in liver, colon, lung, kidney, thyroid, and pancreatic cancer cells. The drug is inactive until cleaved by CES2. Critical to specificity is stability in human plasma predicting stability in the vascular system. The therapy is designed to maximize efficacy and minimize side effects including cardiotoxicity. Very little CES2 is expressed in rat cardiomyocytes and the prodrug is two orders of magnitude less toxic to rat cardiomyocytes than doxorubicin which is commonly used for treatment of HCC. Experiments are designed to improve the synthesis and formulation, to establish a bystander effect for PPD, to measure the pharmacokinetics, and to evaluate the efficacy and toxicity in orthotopic mouse models of HCC. Efficacy endpoints will include tumor growth, survival and pharmacodynamic endpoints of cell proliferation, apoptosis in tumor sections collected after treatment, and Comet assay for DNA crosslinks. Toxicity endpoints will include echocardiogram examination, measures of gross toxicity, white blood cell counts and pathological evaluation of organ tissues following treatment. Preliminary subcutaneous xenograft experiments indicate tumor growth inhibition in mouse models of liver cancer and non-small cell lung cancer using cancer cells that express CES2.